NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This study is based on work supported by Contract NNH06CE15B between the National Academy of Sciences and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the agency that provided support for the project.

THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and Medicine

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council.

Dedication

We dedicate this report to our beloved friend and colleague Steven J. Ostro (1946-2008), who devoted his professional life to the radar study of asteroids and other small bodies in the solar system. His deep understanding, unflagging concentration, and devotion to developing the potential of his junior colleagues led to many significant discoveries on the characteristics, dynamics, and unusual shapes of near-Earth objects.

Preface

The Consolidated Appropriations Act, 2008,1 required NASA to ask the National Research Council (NRC) to conduct a study of near-Earth object (NEO) surveys and hazard mitigation strategies. Near-Earth objects orbit the Sun and approach or cross Earth’s orbit. In a June 2, 2008, letter, James L. Green, director, Planetary Science Division, NASA, and Craig Foltz, acting director, Astronomical Sciences Division, National Science Foundation (NSF), wrote to Lennard Fisk, then chair of the Space Studies Board, requesting that the Space Studies Board, in cooperation with the Aeronautics and Space Engineering Board, conduct a two-part study to address issues in the detection of potentially hazardous NEOs and approaches to mitigating identified hazards (see Appendix B). The ad hoc Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies consisted of the Steering Committee, the Survey/Detection Panel, and the Mitigation Panel.

The statement of task required the committee to include an assessment of the costs of various alternatives, using independent cost estimating. Options that blend the use of different facilities (ground- and space-based) or involve international cooperation were considered. Each study phase resulted in a report to be delivered on the schedule provided below. Key questions addressed during each phase of the study are the following:

Task 1: NEO Surveys

What is the optimal approach to completing the NEO census called for in the George E. Brown, Jr. Near-Earth Object Survey section of the 2005 NASA Authorization Act[2] to detect,[3] track, catalogue, and characterize the physical characteristics of at least 90 percent of potentially hazardous NEOs larger than 140 meters in diameter by the end of year 2020? Specific issues to be considered include, but are not limited to, the following:

What observational, data-reduction, and data-analysis resources are necessary to achieve the Congressional mandate of detecting, tracking, and cataloguing the NEO population of interest?

The committee notes that the statement of task includes the term “detect,” which includes spotting asteroids that have previously been discovered. The committee therefore uses the more appropriate term “discover” to refer to the locating of previously unknown objects.

What physical characteristics of individual objects above and beyond the determination of accurate orbits should be obtained during the survey to support mitigation efforts?

What role could be played by the National Science Foundation’s Arecibo Observatory in characterizing these objects?

What are possible roles of other ground- and space-based facilities in addressing survey goals, e.g., potential contributions of the Large Synoptic Survey Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System (Pan STARRS)?

Task 2: NEO Hazard Mitigation

What is the optimal approach to developing a deflection[4] capability, including options with a significant international component? Issues to be considered include, but are not limited to, the following:

What mitigation strategy should be followed if a potentially hazardous NEO is identified?

What are the relative merits and costs of various deflection scenarios that have been proposed?

NASA and NSF requested an initial report for the first task no later than September 30, 2009. The committee delivered its interim report,5 containing only findings but no recommendations, in early August 2009.

As indicated in Task 1 above, Congress charged the committee to recommend ways to discover and (partially) characterize 90 percent of NEOs exceeding 140 meters in diameter by the year 2020 (smaller objects are not discarded, once found). However, during its first meeting, the committee was explicitly asked by congressional staff to consider whether or not the congressionally established discovery goals should be modified.

Acknowledgments

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Report Review Committee of the National Research Council (NRC). The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Louis J. Lanzerotti, New Jersey Institute of Technology. Appointed by the NRC, he was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

The United States spends approximately $4 million each year searching for near-Earth objects (NEOs). The objective is to detect those that may collide with Earth. The majority of this funding supports the operation of several observatories that scan the sky searching for NEOs. This, however, is insufficient in detecting the majority of NEOs that may present a tangible threat to humanity. A significantly smaller amount of funding supports ways to protect the Earth from such a potential collision or "mitigation."

In 2005, a Congressional mandate called for NASA to detect 90 percent of NEOs with diameters of 140 meters of greater by 2020. Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies identifies the need for detection of objects as small as 30 to 50 meters as these can be highly destructive. The book explores four main types of mitigation including civil defense, "slow push" or "pull" methods, kinetic impactors and nuclear explosions. It also asserts that responding effectively to hazards posed by NEOs requires national and international cooperation. Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies is a useful guide for scientists, astronomers, policy makers and engineers.

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